12 Newbery — Lupton, Radio-activity and Coloration of Minerals. 



most easily decolourised was completely restored after only two 

 days under 25 mg. of radium, while some of the French specimens 

 which had been most difficult to decolourise were not visibly affected 

 by this treatment, and only regained about half their colour after 

 treatment with 50 mg. for ten days. 



One of the most refractory of these decolourised crystals was 

 placed in a tube containing about 20 millicuries of radium emanation 

 and left for twelve days. It had then acquired a reddish grey colour 

 with a peculiar blue fluorescence somewhat similar to that of purple 

 fluor-spar. On warming gently in a test-tube, a bright violet 

 phosphorescent light was emitted and the crystal at once lost its 

 blue fluorescent colour and turned red, the colour being now similar 

 to that originally present. This colour was easily destroyed on 

 further heating. Similarly all the crystals which had been re- 

 coloured by radium, lost their colour at a much lower temperature 

 than had been needed to discharge it before treatment. 



A decolourised crystal placed in a cathode-ray tube glowed 

 with a blue light and regained part of its red colour. 



Beryl. — The natural crystals show considerable variation in 

 colour, from white or colourless, through pale blue (aquamarine) 

 and pale green to the bright green of the precious emerald. 

 Specimens of colourless, pale blue, and pale green beryl were used. 

 The green specimens, from the Mourne Mountains, changed to pale 

 blue on heating in the bunsen flame, while the other specimens were 

 unaltered. 



No change in colour was produced in any of the crystals by 

 radium treatment, but a pale blue crystal, 1 cm. long and about 

 3 mm. diameter, after treatment for ten days with 25 mg. radium, 

 showed a feeble thermo-luminescence. This luminescence was 

 bluish white and appeared on the hexagonal basal planes only, the 

 remainder of the crystal being quite dark. 



Kunzite. — The behaviour was identical with that described by 

 Glew. 



Calcite. — Several colourless specimens from Barrow and Iceland 

 were used, some showing minute cleavage planes and others quite 

 flawless. The latter were unchanged by the action of radium but 

 the former showed considerable multiplication and enlargement 

 of the cleavage planes. 



A very clear flawless crystal glowed with a fine red light under 

 the action of cathode rays, and the glow continued for some time 

 after removal of the crystal from the tube. 



Another specimen from Iceland also glowed both in cathode 

 rays and under radium, but with a much whiter light. In the latter 

 case the warmth of the hand was sufficient to restart the glow 

 after removal from the radium. A third specimen showed a bright 

 yellow thermo-luminescence after radium treatment. 



The variation in colour of the glow appears to indicate that it 

 is due to the presence of impurity and is not an essential property 

 of the pure substance. A piece of native strontianite showed a 

 fine orange-red glow on one part of the mass under the action of 



